Process for the treatment of hydrocarbon oil



INVENTOR.

ATTORNEY M H. ARVESON Fild Dec. 29, 1934 PROCESS FOR THE TREATMENT OF HYDROCARBON OIL I! 0 2 m Q Y No is mv H B I i l 5 N N? T 8 TI w .m u u l mh IN s a Q ,8 N =3 $53 .388

Nov. 23, 1937.

Patented Now. 23, 193 7 PA'IZENT OFFICE PROCESS FOR THE TREATNIENT F HY! DROCARBON OIL Maurice H. Arveson, Highland, Ind., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana Application December 29, 1934, Serial No. 759,620

10 Claims.

This invention relates to .processes for the treatment of hydrocarbon oil and pertains more particularly to processes for producing gasoline or other relatively light distillate from heavy hydrocarbon oil such as crude petroleum oil, re-

' wherein a further separation of the vapors, to

give a plurality of condensates of different boiling ranges, is obtained; these last-mentioned condensates then being subjected to cracking in separate cracking zones under optimum cracking conditions and. the resulting cracked products being combined for further separation and fractionation in the manner already described. In accordance with such prior proposals, the reduced crude resulting from the initial distilling step has either been withdrawn from the process or subjected to an entirely separate single-stage cracking operation.

In accordance with my invention I provide an improved process whereby the fresh charging stock, such as crude oil, is subjected to an initial distillation step wherein it is separated into a plurality of condensate cuts of different boiling point ranges, which may include an overhead condensate of the boiling range desired for the final products, and a reduced crude residue. Each one of these condensate cuts, except that one which is of the desired boiling range for the final product, is passed once through an individual cracking zone wherein it is raised to a cracking temperature and subjected to conversion, all of the resulting cracked products being introduced into a common vapor separating and.

fractionating system, wherein a further separation into a plurality of condensates, including an overhead condensate having the final desired boiling characteristics, and a. residue, occurs. Meanwhile, the residue from the initial distilling operation is subjected to a cracking operation and is introduced into the common vapor separating and fractionating system mentioned.

The cracking of the reduced crude residue may be carried out either by passing the reduced crude through a heating coil in a conventional furnace, wherein it is raised to a cracking temperature and subjected to the desired degree of conversion, or by combining it with one of the stream of hot cracked condensate and then intrcducing the mixture into the separating and fractionating system.

By this procedure, the reduced crude may either be cracked entirely by 971d of heat derived irom the furnace coil. or by contact with the highly heated cracked condensate, prior to the introduction ofthe mixture into the separating and fractionating apparatus. or the heatmg may be carried out first by passage of the oil through the heating coil in the furnace and then by contact with the highly heated cracked condensate. Additional cracking by contact with the highly heated cracked condensate may, be insured by the provision of a soaking drum or reaction chamber in which the mixture of cracked condensate and reduced crude is digested for a sufficient length of time to bring about the desired degree of conversion.

The commingled cracked products are separated, in the vapor separating and fractionating apparatus, into a plurality of condensate cuts of different boiling ranges including an overhead product ialling in the boiling range of the final desired product, and a liquid residue. Condensates so obtained, except gasoline, are separately cracked by being passed once through individual cracking zones and all of the resulting cracked products are introduced into a second vapor separating and fractionating apparatus. Simultaneously the partially cracked liquid residue from the first separating operation is passed through a separate cracking coil and is then-introduced into the second vapor separating appa- 5 ratus, either directly or after having been commingled with highly heated cracked condensate from one of the last-mentioned cracking operations, this commingling preferably taking place in a soaking drum wherein a suiflcient time of 4 reaction is provided to insure the necessary cracking of the reduced crude. Here again part of the cracking may be carried out in the cracking coil and the rest by direct contact of the reduced crude with the highly heated cracked condensate in the soaking drum.

If the liquid residue withdrawn from the first separating zone has too great coke-forming tendencies for eflicient cracking in a furnace coil as mentioned, the residue may be passed instead of through the coil, directly from the-first separating zone into combination with one of the highly heated cracked condensate streams, in a soaking drum as already described. In thiscase all of the cracklng of the residue would-be carried out by heat derived through the direct contact thereof with the highly heated cracked condensate.- According to any one of these alternative methods the resulting cracked residue finds its way into the second separating zone wherein a plurality of condensate cuts of different boiling point ranges and a liquid residue may? be isolated just as described in conneiction with the second. separating and fractionating step. Usually three successive cracking steps -will be found suflicient and usually it .will be desirable to crack the reduced crude in a directly fired coil to effect the first cracking step and then to carry out the next two cracking steps on the residues by direct contact of the residues with highly heated cracked condensates, or. by this procedure coupled with preliminary heating and perhaps partial cracking of the residues in individually directly fired coils.

The vapors from the final cracking step of the series may be fractionated to give a final desired light distillate and one or more reflux condensates which may be withdrawn for sale as distillate fuel oil, or for separate cracking. The.

liquid residue from the final cracking stage of the series may be subjected to a flashing operation in a separate tar flasher and the resulting distillate may be passed through one of the cracking zones mentioned, preferably through one of the zones treating liquid'residue.

Where an intermediate condensate is cracked and used as a heat carrier for aiding in the conversion of liquid residue, the condensate may be of a relativelylight character so that it can be heated to a sufliciently high temperature to carry out the necessary cracking, this light character and high temperature being particularly desirable in the latter stages of the process. The various cracking cells may be located in separate furnaces or in a common furnaceor furnaces, the latter being usually preferable from an initial cost viewpoint. The cracking conditions maintained in the various cracking zones may be selected, in accordance with the teachings of the prior art for the cracking of stocks of like nature. However, as a general rule it is preferable to use relatively high-temperature, short-time cracking conditions for the treatment of the condensate stocks. 1

The above-mentioned and further objects and advantages of my invention and the manner of diagrammatically an oil cracking system embodying my invention. Referring more particularly to the drawing,"

attaining them willbe more fully explained in the following description taken in conjunction with the accompanying drawing.

The single figuremf the drawing represents reference numeral I indicates a crude flash tower and numerals 2, 3 and 4 indicate combination evaporating and fractionating towers. Five '(5) 6, 1, I, 8, 9, 9, l0 and 2!, refer to separate crack ing coils of the directly-fired type which may be located in separate furnaces or in a common furnace or furnaces. 1

Fresh relatively heavy charging stock, such as 33 A. P. I. gravity Mid-continent crude oil, partially reduced crude, or the like, having light as well as heavy constituents, is introduced into tower I through pipe H by action of pump 12, after having been suitably preheated in any well known manner, either by indirect heat exchange with some of the cracked products in succeeding steps of the process, or by passage through a directly-fired coil, to a temperature suflicient to plurality of intermediate condensate cuts are collected, for example two as shown, by aid of trap-out trays l3 and l4. The condensate collected on the former may be a clean gas oil and that collected on the latter may be a heavy naphtha, which it is desired to reform. The gas oil is Withdrawn from tray I3 through pipe I5 and is forced by pump l6 through the heating coil 5 wherein it is raised to a cracking temperature and subjected to conversion. The resulting cracked products pass through the transfer line [1 into the evaporator section I8 of combination tower 2, preferably after having passed through a soaking drum Hi. This drum may be by-passed if desired. At the same time the heavy naphtha is withdrawn from trap-out tray l4 through pipe l9 and is forced by pump 20 through the reforming coil 2| wherein it is raised to a relatively high cracking temperature sufficient to cause the reformation thereof to higher anti-knock gasoline constituents. The reformed products travel through transfer line 22 into the evaporator section l8 in mixture with the other cracked products.

Simultaneously liquid residue is withdrawn from the base 'of the crude flash tower through conduit 23 and is forced by pump 24 through the heating coil 6 wherein it is raised to a cracking temperature and subjected to a viscosity-break-' ing operation, under conditions sufficiently mild to prevent deleterious coke deposition in the heat ing coil. The resulting cracked products are then introduced into the evaporator section l8, preferably directly through the transfer line 25, but alternatively through cross-over line 26 into the soaking drum l9. wherein additional cracking thereof takes place, the resulting vis-broken or moderately cracked reduced crude finally commingling with the other cracked products in the evaporator section I8; Valves 26' and- 28 are inserted in the several transfer lines for pressure control purposes.

In the evaporator section l8 the cracked products separate into vapors and liquid residue, the former passing upwardly through the fractionator section 29 of the combination tower and therein undergoing fractional condensation, while the liquid residue collects in the base of evaporator section l8. A plurality of condensate fractions of different boiling point ranges are collected in the fractionating section, for example two in number, these being collected by trap- The condensate collected on out trays 30 and 3|. the first-mentioned tray 30 may be a relatively light product such as light gas oil, kerosene, or heavy naptha, or a mixture of these, while that collected on the next lower tray 3| may be a clean gas oil condensate of somewhat lower A. P. I. gravity, being in the nature, however, of a clean cracking= stock. I

The condensate is withdrawn from tray 30 through conduit 33, having pump 34, and is forced through the heating coil 1 wherein it is raised to a relatively high cracking temperature and subjected to conversion, the resulting cracked products being introduced into the evaporator section 35 of combination tower 3, through line 36. At the same time condensate is withdrawn from trap-out tray 31 by way of conduit 36', hav-- ing pump 31, and is forced through the heating soaking drum 39 by way of cross-over pipes 42 and 43, for further cracking, or directly into the evaporator section of tower 3, through transfer line 44; or the liquid residue is passed directly through conduit 45 and cross-over line 43 into the soaking drum 39 for cracking, without previously having traversed the heating coil 8. This last-mentioned alternative method is preferred Where the residue has marked cokeforming tendencies such as would tend to make the passage through the heating coil 8 uneconomical.

If desired a trap-out tray 32 may be provided to collect a very heavy, relatively dirty, gasoil condensate which may be recycled to the heating coil 6 by way of pipe line 46 having pump 41. Or this condensate might be collected as mentioned and passed through a separate cracking coil similar to 8 and then be introduced into the evaporator section 35 along with the other stocks. When tray 32 is not used the heavy condensate would pass through heating coil 8 with the residue. I

In the combination tower 3 the cracked products undergo separation into vapors and a liquid residue just as described in connection with the action taking place in tower 2. Trap-out trays- 41', 48 and 49 perform the same function as corresponding elements 30, 3| and 32 in the tower 2.

The condensates collected on trays 41 and 48 are preferably cracked in the coils 9 and 9 and then introduced into the evaporator section 59 of combination tower 4, soaking drum 5| preferably being furnished for the digestion of the cracked products from coil 9'.

The liquid residue from evaporator section 35 of tower 3 is preferably passed directly through conduits 52, 53 and 54 into the soaking drum 5| for cracking, but alternatively may pass first through the heating coil l8 and then into the drum by way of cross-over line 55, or, as a further alternative, may pass directly through the coil l9 and transfer line 56 into the evaporator section of the tower 4. The condensate collected on trap out tray 49 may be recycled to the coil 6 through pipe line 51 having pump 58, or may be passed through an individual cracking coil, not shown, into the evaporator section 50 of the tower 4. Trap-out tray 49 may be omitted if desired, in which case the heavy condensate would pass through heating coil ID with the residue. Reference numerals 59, 68 and 6| indicate pumps for forcing the oils through the cracking coils. Control valves 65, 6|, 62, 63, 64 and 65 are provided for the purpose of adjusting pressure conditions. In the combination tower 4 the cracked products separate into vapors and liquid residue, the latter collecting in the base of the tower, while the former pass upwardly through the fractionating section 66 thereof, wherein fractional condensation occurs, one or several reflux condensates being collected, for example two, trap-out trays 61 and 68 being provided for this purpose.

The condensate from trap-out tray 68 may be withdrawn as a distillate fuel, while condensate from tray 61 is preferably recycled to the heating coil 6 through pipe 69, having pump 18. The liquid residue collecting in the base of the tower is withdrawn through draw-off line H for sale as fuel oil or for any other desired purpose, or this liquid residue may be flashed in a flashing zone, not shown, and the distillate oil obtained may be returned to the heating coil 6. A further alternative would be to combine the condensates from trays 81 and 68 and subject the mixture to a separate cracking operation in an apparatus, not shown, or more simply, to collect only a single condensate in the fractionator section 66 and subject this to separate cracking.

Distillates of the desired boiling ranges. are collected in the receivers 12, 13, .14 and 15, which have cooperating vapor connections 16, 11, I8 and'19, to the towers I, 2, 3 and 4 respectively, and also, condensers 80, BI, 82 and 83. All or some of these distillates before or after stabilization may be blended to give a distillate of selected characteristics for use as motorfuel or for any other purpose. Connections 84, 85 and 86 v are provided so that oil may be withdrawn at these points, or more oil of similar characteristics may be added as desired, to effect balanced operating conditions. Similar connections may be located at corresponding positions adjacent the cracking coils I, I, 8, 9, 9 and ID for like purposes. Various valves shown on the drawing and not indicated specifically by reference numerals are for obvious control purposes. 7 r

The necessary reflux lines, cooling coils and heat exchangers for carrying out the various separating and fractionating operations have been omitted in the interest of clarity but the use of these will be obvious to one skilled in the art. Any conventional arrangements for these purposes may be used.

Where the liquid residue is not combined with a cracked intermediate condensate prior to introduction into a following evaporator zone, it may be desirable to provide for the separate withdrawal of individually cracked tars, this being done by introducing the cracked condensate into a separating zone, not shown, wherein vapors separate from liquid residue, only the vapors being passed to the following combination tower, while the liquid residue so separated is withdrawn from the process for any desired purpose, or is subjected to a separate flashing operation to form additional distillate suitable for further cracking in one of the other cracking coils.

From the foregoing description, it will be seen that the residual stock from the initial and each succeeding cracking operation, is subjected toadditional cracking, as well as the individual intermediate condensate fractions This procedure,

at temperatures in the range of 900 to 975 F.

The heavier residual products passing through coils 6, 8 and I 0 should be cracked at lower temperatures of, for example, 800-880 F. to avoidv excessive carbon deposition.

The pressures used may vary widely but it will generally be found preferable to carry out the cracking of the distillate stocks at relatively high pressures of several hundred pounds per square inch, e. g. 700 to 1100 pounds per square inch. The residual stocks are most suitably cracked at lower pressures, e. g. 100 to '300 pounds per square inch. When the distillate and residual stocks are cracked together in a common soaking zone, the distillate stock may be heated and partially cracked in the coil at high pressure and then be reduced in pressure for contact with the residual stock in the soaking zone. In the high temperature, high pressure heating coils preferably short times of contact are maintained.

The heating coils may advantageously be grouped in common furnace settings, so that all of the low-temperature heating and cracking operations are carried out in one furnace, while the higher temperature heating and cracking operations are carried out in one or more separate furnaces. Thus coils 6, 8 and I0 may be in one furnace, 5, I and 9' in another furnace, and coils 2|, 1 and 9 in a third furnace. Or some or all of the high and low temperature coils may be placed in a single furnace setting, the low temperature coils being mainly in the convection section, and the high temperature coils beingmainly in the radiant section.

While I have described a particular embodiment of my invention for the purposes of illustration, it should be understood that various modifications and adaptations thereof may be made within the spirit of the invention as set forth in the following claims.

I claim:

1. The process of treating hydrocarbon oil which comprises subjecting heavy oil to distillation to form a condensate fraction and a liquid residue, cracking said condensate and said liquid residue by passing each through a separate heat- :Ing zone in a stream of restricted cross-sectional area wherein a cracking temperature is attained and conversion occurs, introducing the resulting cracked products into a first separating zone wherein vapors separate from liquid residue, subjecting said vapors to a fractionating operation to form a final desired distillate and a reflux condensate, subjecting said reflux condensate to cracking by passing it through a heating zone in a stream of restricted cross-sectional area wherein said condensate is raised to a. cracking temperature and subjected to conversion, combining the resultant stream of hot cracked products with saidiiquid residue last mentioned and maintaining the combined constituents at a cracking temperature to effect conversion of said liquid residue, introducing the resulting cracked products into a second separating zone wherein vapors separate.

from liquid residue and fractionating said vapors to form an additional light distillate.

2. A process in accordance with claim 1 wherein in the fractionation of the vapors separated in said second separating zone lighter and heavier reflux condensates are formed, the lighter reflux condensate constituting the condensate that is passed through said heating zone, and the heavier reflux condensate is combined with said residue first-mentioned for further treatment.

3. A process in accordance with claim 1 wherequantity of final desired in said liquid residue second-mentioned is passed through a heating zone in an individual stream of restricted cross-sectional area wherein the temperature thereof is increased prior to the mixture thereof with said cracked reflux condensate.

4. The process of treating hydrocarbon oil which comprises subjecting crude oil to a preliminary distillation to form a condensate fraction and a liquid residue, separately cracking said condensate and said liquid residue by passing each through-a heating zone in a stream of restricted cross-sectional area wherein a cracking temperature is attained and conversion occurs, introducing the resulting cracked products into a first separating zone wherein vapors separate from liquid residue, subjecting said vapors to a fractionating operation to form a final desired distillate and a reflux condensate, subjecting said reflux condensate to cracking by passing it through a heating zone in a stream of restricted cross-sectional area. wherein said condensate is raised to-a cracking temperature and subjected to conversion, combining the resultant stream of hot cracked products with said liquid residue last mentioned and maintaining the combined constituents at a cracking temperature to effect conversion of said liquid residue, introducing the resulting cracked products into a second separating zone wherein vapors separate from liquid residue, fractionating said vaporsto form an additional quantity of final desired light distillate and a refiux condensate, passing said reflux condensate last mentioned through a heating zone in a stream of restricted cross-sectional area wherein it is raised to a cracking temperature and subjected to conversion, combining the resultant stream of hot cracked products with said liquid residue last mentioned and maintaining the combined constituents at a cracking temperature to effect conversion of said liquid residue, introducing cracked products so obtained into a third separating zone wherein vapors separate from liquid residue, and fractionating said vapors lastmentioned to form an additional quantity of final desired light distillate.

5. A process in accordance with claim 4 wherein during said preliminary distillation step a heavy naphtha condensate is collected and passed through a heating zone in an individual stream of restricted cross-sectional to a relatively high cracking temperature suflicient to cause the reformation thereof into products of higher anti-knock value, and the resulting reformed products are introduced into said first separating zone.

6. The process of treating hydrocarbon oil which comprises subjecting said oil to cracking in a plurality of successive stages, each of which stages includes a heating coil, a reaction chamber, a separator, and a fractionator, the heating coil, reaction chamber, separator and fractionator of each stage being separate, respectively, from those of the other stages, the charge to each cracking coil being a clean condensate stock which, after area wherein it is raised being raised to a cracking temperature, is combined with a liquid residue stock and introduced into the reaction chamber, the resulting digested products passing into the separating zone and the charge to the cracking coil in stages following the first, being a condensate stock formed in the iractionator of the preceding stage, and the residue introduced into the reaction chamber with the cracked condensate from the cracking coil last-mentioned, being liquid residue from the separator of the preceding cracking stage, and the final desired product being derived by condensing light fractionated vapors from said fractionators.

7. The process of treating hydrocarbon oil which comprises fractionally distilling in a distilling zone fresh relatively heavy charging stock containing lighter constituents to form a clean condensate cracking stock and an unvaporized residue, simultaneously passing said condensate and said residue through separate cracking zones wherein they are raised to cracking temperatures and subjected to conversion, introducing the resulting cracked products into a first separating zone, separate and apart from said distilling zone, wherein vapors separate from liquid residue, passing the separated vapors into a fractionating zone, also separate and apart from said distilling zone, and fractionally condensing said vapors therein to form a second condensate, passing said second intermediate condensate through a separate cracking zone wherein it is raised to a cracking temperature and subjected to conver-- sion, introducing the resulting cracked products into a second separating zone, separate and apart from said distilling zone, wherein vapors separate from liquid residue, passing the separated vapors into a second fractionating zone, also separate and apart from said distilling zone, and fractionally condensing said vapors last-mentioned therein to form a final desired light distillate and a heavy reflux condensate, and combining said condensate last-mentioned withsaid unvaporized residue first-mentioned for cracking therewith.

8. A process in accordance with claim 6 wherein the first stage also includes a second heating coil and the liquid residue stock for the first stage is introduced into said second coil for mild cracking prior to being combined with the clean condensate stock.

9. A process in accordance with claim 6 wherein the first stage also includes a second heating coil and the liquid residue stock for the first stage is combined with a heavy reflux condensate from the iractionator of the last stage and introduced into said second coil for mild cracking prior to being combined with the clean condensate stock.

10. The process of treating hydrocarbon oil which comprises fractionally distilling fresh relatively heavy charging stock containing lighter constituents to form a clean condensate cracking stock and an unvaporized residue, simultaneously passing said condensate and said residue through separate cracking zones wherein they are raised to cracking temperatures and subjected to conversion, introducing the resulting cracked products into a first separating zone wherein vapors separate from liquid residue, fractionally condensing said vapors to form a second condensate, passing said second condensate and said residue last mentioned through separate cracking zones whereinthey are raised to cracking temperatures and subjected to conversion, introducing the resulting cracked products into a second separating zone wherein vapors separate from liquid residue, fractionally condensing said vapors last-mentioned to form a final desired light distillate and a heavy reflux condensate, and combining said condensate last-mentioned with said unvaporized residue first-mentioned for cracking therewith.

MAURICE H. ARVESON. 

